In general, there is known a fuel injection apparatus for internal combustion engine which feeds fuel from a single fuel injection portion to all cylinders of an internal combustion engine.
This known fuel injection apparatus for internal combustion engine is constructed as follows. A throttle valve is provided in an air-intake path connected to the upstream side of an air-intake tube meeting portion communicating with each cylinder, and a fuel injection portion is provided on the upstream side of this throttle valve. Also, an electromagnetic valve forming the fuel injection portion is driven by a pulse with a certain width to intermittently inject fuel into the air-intake path. This valve opening pulse is controlled in its width by an air-intake amount signal which is detected by an air flow meter provided in the air-intake path.
This known fuel injection apparatus has the following drawbacks:
(1) Since the fuel injection portion intermittently injects fuel into the air-intake path connected to the upstream side of the air-intake tube meeting portion, thick and thin air-fuel mixture portions are alternately formed between the air-intake path and the air-intake tube meeting portion, that is, the air-fuel mixture becomes ununiform in space. Thus, when the cylinders of the internal combustion engine sequentially intakes the air-fuel mixture, some cylinder intakes a thick mixture and another one does a thin mixture, that is, the distribution property of fuel is poor. This causes variation of torque in the internal combustion engine.
(2) Since the air flow meter is used to measure the amount of air intake and determine the valve opening pulse width over a wide range from idling drive to high-speed, high-load drive, the precision of the air flow meter is required over the wide range. In other words, the air flow meter must practically detect the true amount of air taken in the internal combustion engine over the wide range from idling drive to high-speed, high-load drive. This requires a high-precision air flow meter over a wide range and causes a signal processing circuit connected to the output of the air flow meter to be complicated in construction.